The present invention relates to a gas turbine system, which permits to monitor occurrence of flashback of combustion gas on the basis of data of NOx concentration detected from the combustion gas.
A combined cycle power generation system has characteristic properties such as an improved plant thermal efficiency, a reduced start-stop time, decreased amounts of hot drainage and the like, which have been highly rated. The combined cycle power generation system has recently become one of the leading mainstreams of the latest thermal power plants.
The combined cycle power generation system is composed of a gas turbine system, a steam turbine system and a heat recovery steam generator in a tandem or single shaft arrangement, so that utilization of exhaust gas from the gas turbine system as heat source for the heat recovery steam generator causes the boiler to generate steam, and the thus generated steam is supplied to the steam turbine system to generate power. The exhaust gas from the gas turbine system can be utilized thoroughly, leading to a remarkably high plant thermal efficiency in comparison with the gas turbine system alone or the steam turbine system alone.
There has recently been made a reassessment of a gas turbine-combustor to be incorporated into the combined cycle power generation system having a high plant thermal efficiency, in view of prevention of pollution of the environment. Such a reassessment is made with an eye to monitoring of combustion condition of combustion gas and reduction in NOx concentration.
The former technical measures, i.e., to monitor the combustion condition of the combustion gas have conventionally been proposed. One of these measures is disclosed in Japanese Laid-Open Patent Publication No. SHO 53-82909.
Such a prior art exemplifies a gas turbine system alone as shown in FIG. 6. In the prior art, temperature of exhaust gas from an exhaust gas duct 2 of a gas turbine 1 is detected by means of a plurality of thermocouples 3. An intermediate temperature (i.e., a median temperature) is calculated from the detected temperatures. A comparison is made between the intermediate temperature and the individual temperatures actually detected. When deviation exists between the former and the latter, or the deviation exceeds a prescribed value, a combustion monitoring device 4 judges combustion condition of the combustion gas. In case where the combustion monitoring device judges the combustion to be xe2x80x9cimproperxe2x80x9d, it supplies an alarm signal ALM or an operation shutdown command TRP to a gas turbine control device 5 to control a fuel valve 6 so as to be opened or closed. The above-described prior art, which is based on a theory that abnormal combustion is always revealed as decrease in temperature of the exhaust gas, has been put to practical use.
Japanese Laid-Open Patent Publication No. SHO 59-134332 for example discloses the latter technical measures, i.e., to reduce the NOx concentration.
Such a prior art exemplifies a combined cycle power generation system as shown in FIG. 7, in which diffusion combustion is applied as a combustion system for a gas turbine-combustor 7. In the prior art, a NOx concentration sensor 10 is provided on the downstream side of a catalyst 9 of a heat recovery steam generator 8 in the flowing direction of the exhaust gas. A NOx concentration value signal P detected by means of the NOx concentration sensor 10 is compared with a predicted NOx concentration value signal Q from a NOx concentration predictor 11 integrated into a gas turbine control device 5, in an NH3-injection control system 12 to make a calculation. On the basis of the calculation result, an amount of ammonia to be supplied is calculated. Ammonia is supplied in an amount thus calculated into, for example, an exhaust gas duct 2 connecting a gas turbine 1 and the heat recovery steam generator 8 with each other. In addition, a valve opening of a fuel valve 6 is controlled to adjust the flow rate of fuel, thus maintaining a low NOx concentration.
The technical measures as shown in FIGS. 6 and 7 concerning the monitoring of combustion condition of the combustion gas and the reduction in NOx concentration have already been put into practice, thus contributing prevention of the pollution of the environment. Especially, according to the technical measures as shown in FIG. 7, there is provided a high precision of prediction of the NOx concentration even with the use of calculation measures in case of a diffusion combustion, thus becoming one of the excellent measures in the field of art.
Gas turbine-combustors providing an extremely low NOx concentration have recently been demanded due to the further enhanced environmental regulation against the NOx concentration. With respect to such a demand, the diffusion combustion type gas turbine-combustors as shown in FIGS. 6 and 7 have already reached their limits. In view of this fact, dry type premixing lean combustion type gas turbine-combustors have alternatively been put into practice as service equipment.
According to the dry type premixing lean combustion, air is previously added into fuel to provide a lean-fuel condition and burned under such the lean-fuel condition to reduce a flame temperature, thus reducing the NOx concentration so as to completely conform to legally regulated values.
However, the dry type premixing lean combustion type gas turbine-combustors, which are excellent in reduction in the NOx concentration, even have some problems. One of these problems is a phenomenon of flashback (backfire) of the combustion gas.
The problem of flashback of the combustion gas is inherent in the dry type premixing lean combustion system. With respect to the flashback, sudden ignition occurs in a lean-fuel premixing zone, causing flame temperature to increase locally. As a result, there is generated the combustion gas having a high NOx concentration.
It is conceivable to apply the technical measures for calculation as shown in FIG. 7 to predict the NOx concentration from temperature distribution of the exhaust gas as the device for monitoring such a phenomenon.
However, flame of the flashback, which occurs in the lean-fuel premixing zone, then reaches the combustion zone to flow into flame in the combustion zone. It is difficult to judge increase in NOx concentration due to the flashback from the temperature distribution of the exhaust gas, even when the above-mentioned technical measures for calculation is applied. If the flashback is not detected, operation continues in the presence of the flashback, leading to a possible burnout accident of the gas turbine-combustor.
For these reasons, the realization has been demanded of the combustion monitoring device suitable for the dry type premixing lean combustion.
An object of the present invention, which has been made in view of the above-described problems, is therefore to provide a gas turbine system that makes it possible to surely detect a flashback of fuel gas in a gas turbine-combustor through NOx concentration of an exhaust gas measured.
This and other objects can be achieved according to the present invention by providing, in one aspect, a gas turbine system which comprises a compressor, a gas turbine-combustor, a gas turbine and a generator, which are operatively connected in series, a combustion monitoring device for detecting NOx concentration of an exhaust gas to be exhausted from the gas turbine so as to monitor combustion condition of the combustion gas in the gas turbine-combustor, and a gas turbine controller operatively connected to the combustion monitoring device and provided with a NOx value predictor,
the combustion monitoring device comprising:
an alarm signal calculation circuit for operating an alarm signal based on the NOx concentration detected from the exhaust gas at a time when flashback of the combustion gas in the gas turbine-combustor occurs to reach a premixed combustion zone;
a shutdown calculation circuit for operating a shutdown command when the flashback grows into a prescribed scale; and
a flashback-error signal prevention calculation circuit for compensating signal delay of the NOx concentration detected from the exhaust gas in accordance with a predicted NOx concentration value signal from the NOx value predictor.
In a preferred embodiment of this aspect, the alarm signal calculation circuit comprises a calculation element for comparing a real NOx concentration value signal detected from the exhaust gas with the predicted NOx concentration value with the NOx value predictor so as to make a calculation, a comparator for making a signal at a time when an operation signal from the calculation element exceeds a predetermined value, and an AND circuit for operating the alarm signal when the operation signal from the comparator coincides with an operation signal from the flashback-error signal prevention calculation circuit.
The shutdown calculation circuit comprises a calculation element for comparing a real NOx concentration value signal detected from the exhaust gas with the predicted NOx concentration value from the NOx value predictor so as to make a calculation, a comparator branching off from an output side of the calculation element for making a signal at a time when an operation signal from the calculation element exceeds a predetermined value, and an AND circuit for operating the shutdown command at a time when the operation signal from the comparator coincides with an operation signal from the flashback-error signal prevention calculation circuit.
The flashback-error signal prevention calculation circuit comprises a differentiator for making a calculation in response to a fuel gas valve control command from the gas turbine controller, a comparator for making a signal at a time when an operation signal from the differentiator exceeds a predetermined set value, and a timer for holding an operation signal from the comparator by a predetermined period of time.
Both the alarm signal from the alarm signal calculation circuit and the shutdown command signal from the shutdown calculation circuit are generated during a prescribed loaded operation.
The gas turbine controller is provided with an NH3 injection control system.
In a second aspect of the present invention, there is also provided a gas turbine system which comprises a compressor, a gas turbine-combustor, a gas turbine and a generator, which are operatively connected in series, a combustion monitoring device for detecting NOx concentration of an exhaust gas to be exhausted from the gas turbine so as to monitor combustion condition of combustion gas in the gas turbine-combustor, and a gas turbine controller operatively connected to the combustion monitoring device,
the combustion monitoring device comprising:
an alarm signal calculation circuit for operating an alarm signal based on the NOx concentration detected from the exhaust gas at a time when flashback of the combustion gas in the gas turbine-combustor occurs to reach a premixed combustion zone;
a shutdown calculation circuit for operating a shutdown command at a time when the flashback grows into a prescribed scale; and
a delay prevention calculation circuit for calculating NOx concentrations of a plurality of previous periods of all previous periods of a current NOx concentration detected from the exhaust gas so as to compensate signal delay of the current NOx concentration.
In a preferred embodiment of this aspect, the alarm signal calculation circuit comprises a calculation element for compairing the current NOx concentration value signal with the NOx concentrations of the previous periods calculated by the delay prevention calculation circuit to calculate a range of variation of a real NOx concentration, and a comparator for making a signal to send the alarm signal at a time when a calculated range of variation of the real NOx concentration exceeds a predetermined value.
The delay prevention calculation circuit is branched off from an output side of an inlet end of the alarm signal calculation circuit and is connected to the calculation element of the alarm signal calculation circuit.
The delay prevention calculation circuit includes a plurality of delay units for calculating NOx concentrations of a plurality of previous periods of all the previous periods of a current NOx concentration detected from the exhaust gas.
Both the alarm signal from the alarm signal calculation circuit and the shutdown command signal from the shutdown calculation circuit are generated during a prescribed loaded operation.
In a further aspect of the present invention, there is also provided a gas turbine system which comprises an air compressor, a gas turbine-combustor, a gas turbine and a generator, which are operatively connected in series, a heat recovery steam generator operatively connected to the gas turbine, a combustion monitoring device for detecting NOx concentration of an exhaust gas to be exhausted from the gas turbine so as to monitor combustion condition of combustion gas in the gas turbine-combustor, and a gas turbine controller operatively connected to the combustion monitoring device and provided with a NOx value predictor,
the combustion monitoring device comprising:
an alarm signal calculation circuit having a NOx sensor disposed on an upstream side of a catalyst disposed to the heat recovery steam generator for detecting the NOx concentration of the exhaust gas, the alarm signal calculation circuit operating an alarm signal based on the NOx concentration detected by the NOx sensor at a time when flashback of the combustion gas in the gas turbine-combustor occurs to reach a premixed combustion zone;
a shutdown calculation circuit for operating a shutdown command at a time when the flashback grows into a prescribed scale; and
a flashback-error signal prevention calculation circuit for compensating signal delay of the NOx concentration detected by the NOx sensor in accordance with a predicted NOx concentration value signal from the NOx value predictor.
According to the gas turbine system of the present invention of the structures and characters mentioned above, the alarm signal calculation circuit, the shutdown calculation circuit and the flashback-error signal prevention calculation circuit are integrated in a diagnostic circuit for monitoring occurrence of flashback into the lean-fuel premixing zone of the gas turbine-combustor so as to prevent the flashback-error signal from being generated. It is therefore possible to carry out a safety operation of the gas turbine-combustor.
Furthermore, according to the gas turbine system of the present invention, the shutdown calculation circuit and the delay prevention calculation circuit are integrated in the diagnostic circuit for monitoring occurrence of flashback into the lean-fuel premixing zone of the gas turbine-combustor so as to compensate for a signal delay of the real NOx concentration value signal. It is therefore possible to surely detect the flashback in the gas turbine combustor even during load variation.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.